The present invention relates to a fuel injection system and a fuel injection valve driving method.
An overexciting current and a holding current for driving a fuel injection valve have conventionally been set to fixed values. Because of a need for a reduction in exhaust emissions, however, there are now requirements for expanding a dynamic range of fuel injection amount control and for an extremely small amount of fuel injection. To meet these requirements, there is known a method as disclosed, for example, in Japanese Patent Laid-open No. Hei 6-241137, in which the overexciting current and the holding current supplied to the fuel injection valve are varied in accordance with a fuel supply pressure detected by a fuel supply pressure detector.
The fuel injection valve driving method by means of the fuel supply pressure detector, however, involves various types of delay including a response lag of the fuel supply pressure detector, a lag produced by a noise filter of a signal processing circuit, and a lag produced by a software filter provided in an arithmetic unit. More specifically, because of these delay factors involved, a lag is generated in detection of the fuel supply pressure despite the fact that the fuel supply pressure is, in reality, already high. As a result, a lag is produced in increasing the value of current supplied to the fuel injection valve. Then, no attractive force for overcoming the fuel supply pressure is generated in the fuel injection valve. That is, a condition arises, in which fuel is not injected because of the fuel injection valve not being opened.